1. Field of the Invention
The present invention relates generally to self-propelled mowers, and more particularly, to an automatic tensioning device for a drive train, which drivingly connects a ground wheel to the mower transmission, wherein the tensioning device prevents retrograde slackening of the drive train caused by shock forces or reversing the directional movement of the train.
2. Discussion of the Prior Art
Conventionally, self-propelled mowers are provided with one or more driven ground wheels which are drivingly connected to the mower transmission by a drive train, such as a chain or belt drive. In a vast majority of these known constructions, the transmission is geared so that the drive train and ground wheel are reversible. Further, mower transmissions are often the means for braking the ground wheel. In mowers having two driven ground wheels, wherein each wheel has an independent transmission and speed control, the reversible ground wheels provide steering and bi-directional movement of the mower. The ornamental appearance of such a mower has been claimed in co-pending application Ser. No. 29/012,525, filed Sep. 3, 1993, in the names of Donald F. Crosby, et al., which is assigned of record to the assignee of the present application.
In both the unidirectional and reversible constructions, the drive train connecting the ground wheel with the mower transmission typically includes a drive pulley or sprocket, a driven pulley or sprocket, and a flexible, endless element entraining the sprockets or pulleys. Traditionally, an idler assembly having an idler arm and rotatable idler pulley or sprocket is biased in a tensioning direction to take up slack of the element as it stretches due to wear or loading conditions. Removal of slack tends to prevent the element from coming off the pulleys or sprockets and provides quicker transition from forward to reverse. In the case of a belt drive, the idler assembly is further biased to apply a sufficient tensioning force against the element so that torque is transmitted from the drive pulley to the driven pulley.
The idler assembly is commonly disposed so that the idler pulley or sprocket applies a tensioning force against the slack run of the element as the drive train moves in a forward direction, which corresponds with forward movement of the mower. However, with transmissions that provide braking power for the ground wheels, braking causes the slack run to tighten, which resists the tensioning bias of the idler. Further, in the case of a reversible drive train, when the train direction is reversed, the slack run becomes taut, which similarly resists the tensioning bias of the idler. In instances of a relatively weak idler bias, such as with chain drives, the now taut run of the element moves the idler in a retrograde slackening direction. However, in order to maintain driving connection between the pulleys or sprockets in the reverse direction, take up of the slack must continue and the tension must be maintained.
Accordingly, idler assemblies have been provided with biasing springs that over-tension the element as it moves in the forward direction, so that a residual bias prevents slackening of the element and maintains tension on the element when it shifts to the reverse direction. However, over-tensioning of the flexible element often leads to shortened element life. Alternatively, devices have been developed for reversible drive trains that maintain tension on the element and prevent retrograde slackening thereof without over-tensioning the element as it moves in a forward direction. Such devices are often configured similar to a conventional idler assembly but having a biased idler sheave for applying a tensioning force against the drive train element and a locking mechanism for preventing the sheave from moving in a retrograde slackening direction; both components being a single complex structure. Additionally, devices have been provided having a pair of tensioning pulleys, each being associated with opposed runs of the element. The tensioning pulleys are operably coupled so that at any given time, only one of the tensioning pulleys applies a tensioning force against an associated slack run of the element. As the direction of the element alternates from forward to reverse, the tensioning pulleys independently apply a tensioning force against alternating slack runs of the element. However, these conventional devices, which were developed to prevent over-tensioning of the element of a reversible drive train while taking up slack in both the forward and reverse direction, are considerably complex and expensive. Further, such devices are not capable of being used with conventional idler assemblies.